Method of controlling the exhaust of gases from a metal refining bath



5 Nov. 16, 1965 J. DUMONT-FILLON 3,218,158 METHOD OF CONTROLLING THE EXHAUST OF GASES FROM A METAL REFINING BATH 35 m Duuour-fiuau new Nov. 16, 1965 J. DUMONT-FILLON 3,218,158

METHOD OF CONTROLLING THE EXHAUST OF GASES FROM A METAL REFINING BATH 3 Sheets-Sheet 2 Filed March 8, 1963 Mun/rat.

im QUES DU/fO/ILE L 0N new" Nov. 16, 1965 J. DUMONT-FILLON 3,218,158

METHOD OF CONTROLLING THE EXHAUST OF GASES FROM A METAL REFINING BATH 3 Sheets-Sheet 3 Filed March 8, 1963 a m M W m a M J w 4 m w I 0 am W D 6 0.. n/ a E m. um Q I 5 Q m Q: mw -\Q (mm Sm O Q HI. 0 3% \Q 1g F m 8 m S 3,218,158 METHOD OF CONTROLLING THE EXHAUST F GASES FROM A METAL REFINING BATH Jacques Dumont-Fillon, Metz Queuleu (Moselle), France, assignor to Institut de Recherches de la Siderurgie Francaise, Saint Germain-en-Laye, France, a professional institution of France Filed Mar. 8, 1963, Ser. No. 263,919 Claims priority, application France, Mar. 14, 1962, 891,031, Patent 1,325,023 3 Claims. (Cl. 7560) The present invention relates to the control of the flow of exhaust gases emanating from a metal refining bath, such as a converter in an oxygen process of steel making, and more particularly to a method wherein the exhaust gases are withdrawn through a hood slightly spaced from the converter mouth and combustion of the withdrawn gases by contamination with the surrounding air is prevented by keeping the pressure differential between the surrounding atmosphere and the exhausted gases at the base of the hood at zero whereby no air enters into the hood.

An exhaust method and apparatus based on this principle has been disclosed and claimed in copending application Serial No. 147,543, filed October '25, 1961, by Marc Allard for Exhaust for Steel Converter and assigned to the assignee of the present application. The control method of this application may be applied to the system disclosed in the copending application, wherefore the same will not be discussed in detail herein, full reliance being had for all pertinent details on the teaching of the prior application.

In short, the exhaust system to which the control method of the present invention is applied comprises the collection of a hot fluid stream of effluent emanating into the atmosphere from a steel converter or like metal refining apparatus in a hood which is slightly spaced from the mouth of the converter whereby a space is left between the base of the hood and the converter mouth, exhausting the collected eflluent from the hood while cooling it, and so controlling the exhaust suction that the fluid pressure in the space is maintained at a value substantially identical with that of the surrounding air.

In this manner, while the hood does not prevent the visible observation of the fumes and flames at the converter mouth, the balanced pressure between the atmosphere and the interior of the hood at the interspace between converter mouth and hood base prevents any air from entering and mixing with the hot fluid eflluent, thus eliminating the danger of combustion, or any effluent from diffusing into the atmosphere.

However, it has become apparent in the operation of this exhaust system that it is exceedingly diflicult, if not impossible, to measure the fluid pressure at the base of the hood because the pressure gages must be surrounded by the hot efliuent to be exhausted. Therefore, the fluid pressure has to be taken at a higher level within the hood and the real pressure at the base of the hood must be deduced from the measured pressure in the hood. Experience has shown that any deviation of the pressure differential from zero in the interspace, even as little as 1.5 or 2 mm. of water, for example, causes entry of air into the eflluent stream and/or escape of the hot effluent into the atmosphere, depending on where the excess pressure is.

It is the principal object of the present invention to avoid this difliculty and constantly to control the exhaust suction so that the fluid pressure at the entrance to the exhaust hood is at all times in equilibrium with the atmospheric pressure surrounding it.

- This and other objects are accomplished by calculating nit-ed States Patent 0 3,218,158 Patented Nov. 16, 1965 the pressure at the base of the hood on the basis, and as a function, of the fluid pressure effectively measured at a higher point in the hood and the fluid volume flowing through the hood in a unit of time, or flow rate.

More particularly and preferably, the exhaust suction is controlled in dependence on the fluid pressure differential at the base of the hood calculated on the basis of the following equation wherein AP, is the pressure differential at the base of the hood, AP is the fluid pressure differential measured at a higher point in the hood, A and K are empirical constants, and Q is the volume of gas flow in the hood.

If desired, account may also be taken of the temperature of the fluid efiiuent in the hood, according to the following formula wherein the same symbols designate the same parameters as in Equation I:

k being another empirical constant, T, being a reference temperature and T being the efliuent temperature in the hood.

Throughout the specification and the claims, fluid pressure differential means the difference between the fluid pressure at a given point or level, for instance at the base of the hood, and the atmospheric pressure surrounding this point or level at a given time.

As indicated hereinabove, effective operation of the exhaust system requires the exhaust suction to be always so regulated that AP =0. According to this invention, the fluid pressure differential AP is measured and AP, is computed as a function of AP and parameters X, Y, Z, etc. of the exhaust system operation, such as the eflluent flow, its temperature, its composition, etc.

In actual operation, it has been found that AP, is related to AP substantially only in dependence on the flow volume Q of the effluent passing through the hood and that the other factors, such as the temperature in the hood in particular, may often be entirely neglected. It has been found that if the Equation I is fed to a relatively simple computer, this very often suflices to obtain the desired control of the exhaust suction. In some instances, however, it may be necessary to take other factors into consideration, too, in which case a somewhat more complex computer is required to take into account, for example, the temperature of the outflowing gas. This may be measured conveniently at the exit of the hood by means of a very sensitive thermocouple.

There are, of course, many practical ways of operating according to the principles of the present invention. For example, a conventional exhaust suction control may be used, such as fully disclosed in the above-mentioned copending application, and a computer may be interposed between the point of measuring the pressure differential and the suction control means, the computer output actuating the control means automatically in a manner well known in the art of automation. In this manner, the control means receives the parameter AP, obtained by the computer from the parameter AP and thus constantly holds the exhaust suction to a value maintaining the pressure differential between the interspace separating the hood from the converter mouth and the surrounding atmosphere at zero.

It is also possible directly to transmit the parameter .AP to the exhaust suction control and to displace its actuating point according to the indications received from the computer which produces a correction parameter AP -AP In this embodiment, the directly controlled parameter AP is no longer maintained constant by the control means.

In yet another embodiment, a conventional control device may be replaced by a computer which constantly solves the equations guiding the operation of the device, including Equation I, whereby the exhaust suction force is calculated constantly as the operation proceeds and thus an absolutely flawless operation is assured by keeping the pressure differential at the base of the hood absolutely and at all times at zero.

Obviously, all these and many other means of controlling the exhaust suction wil be used by the skilled in the art on the basis of practical operating conditions and the present invention is not limited to any specific means for accomplishing this purpose.

The objects, features and advantages of this invention will be more fully understood in connection with the following detailed description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawing wherein FIG. 1 is a chart showing curves at different temperatures, which relate the parameters AP AP and the flow volume Q;

FIG. 2 is a diagrammatic view of the exhaust installation for an efiluent from a steel converter operated according to the invention; and

FIG. 3 is a schematic view and circuit diagram of the control means in the installation of FIG. 2.

FIG. 1 shows curves of the pressure differential AP -AP as a function of the gas volume Q flowing through the hood, three curves for the respective gas exit temperatures of 750 (3., 850 C. and 900 C. being given. These temperatures were measured at the exit of the hood into the exhaust conduit and the exhaust system was used for conducting away and cooling the eflluent gases from a steel converter of five tons capacity and operating in an oxygen process. The pressure variations are indicated in millimeters of water and the gas flow volume in standard cubic meters per minute.

The following numerical values may be deduced from these curves for Equation 1 AP :AP A -KQ A2030 and K:0.0005 for 850 C.

Thus, AP ::AP O.300.O005Q P P and A being expressed in mm. of water and Q in standard cu. m./min,

Taking into account also the influence of the temperature, another corrective parameter may be introduced according to Equation 11, i.e. MT -T). For TOT-850 (3., FIG. 1 indicates the constant k;:0.001.

Thus, Equation II reads FIG. 2 schematically illustrates an exhaust installation for conducting and cooling effluent gas safely from the steel converter 1, the efiluent fluid discharge from the converter being nomally of relatively great volume and of relatively high temperature, and containing dust, smoke, fumes, etc. As shown, an eflluent exhaust hood 2 is mounted above, and vertically spaced from, the mouth of the converter, with its exit or outlet leading into exhaust conduit 3. An interspace is left between the base of the hood and the converter mouth, through which air from the surroundingatmosphere could enter or efliuent could diffuse into the surrounding atmosphere it the pressure ditferential at this point were not maintained at zero so that no lateral gas flow occurs.

The exhaust conduit 3 leads into a dust removing humidifier 4 built as a venturi. While the eflluent is exhausted through this system, it is simultaneously cooled by jacketing the hood and the conduit and continuously flowing a cooling fluid, such as water, therethrough. The eflluent is exhausted by the suction force exerted by blower 5 whose input is connected to the humidifier 4 and whose output conducts the dust-free gas, composed primarily of carbon monoxide, to a chimney 7 where it is burned.

With a constant speed of the blower, the exhaust suction force is controlled by butterfly or throttle valve 6 arranged in the exhaust conduit and controlling the gas flow therethrough. 5 The pressure differential AP is measured at a given level within the hood 2 by three tubes 9a, 9b, 9c connected in series to one chamber of a pressure differential indicator 8 with a flexible membrane and, at the same level, by a tube it in the surrounding atmosphere and connected to the other chamber of the indicator 8. This indicator is fully described in the copending application, which forms part of the present disclosure, and includes an eletromagnetically displaceable transmitter which furnishes an electrical signal proportional to the pressure differential by means of an interposed electrical generator and demodulator ill.

The temperature of the eifluent at the outlet of the hood 2 is measured by a thermocouple 12 placed at the inlet or entry of exhaust conduit 3.

The efiiuent volume flow is measured after the eflluent has been cooled and made dust-free by conducting the cooled and cleaned gas through venturi 13 in chimney 7, rue venturi being in communication with an electric flowmeter 14, automatically corrected for pressure, temperature and humidity. This flowmeter actually is a differential manometer measuring the depression caused in venturi 13 and transmitting its reading electrically.

The electrical signals from generator-demodulator 11 (indicating the pressure differential AP obtained from tubes 9a, 9b, 9c and iii), from thermocouple 12 and from the electric flowmeter 1 are transmitted by the control circuit consisting of lines 41, 42 and 43 to the electronic computer l5 which correlates the pressure differential, the temperature and the eflluent flow volume to produce an AH, according to Equation II. The resultant output signal indicating the actual pressure differential AP, at the base of the hood 2, where it cannot be measured, is fed to a potentiometer 16 provided with a conventional pneumatic governor 17 which controls the position of valve 6 so that the pressure differential AP, constantly remains at zero. All of this control mechanism may be entirely conventional and an illustrative embodiment thereof is fully described in the copending application mentioned hereinabove.

The structure and operation of the electronic computer will be described hereinafter in connection with the circuit diagram of FIG. 3. As shown, the atmospheric pressure taking tube it leads into chamber 8' of the pressure differential indicator 3 while the tubes 9a, 9b, 90, which take the efliuent pressure within the hood at the same level as tube it lead into the other indicator chamber 8", the two chambers being separated by flexible membrane or diaphragm 3a. A magnetic core, 8b for instance of iron, is connected to the membrane 8a and is reciprocated between pick-up coils 80 by any pressure diflerential in indicator chambers 8', 8 causing the membrance 8a to be flexed. Reciprocation of core 812 will vary the impedance in coil 80 constituting an electromagnetic transmitter. The coil 80 is fed by an oscillator 11a which delivers current at 1000 c.p.s. The signal delivered by the transmitter 8c is demodulated by a conventional electronic demodulator lilb and the output voltage of the demodulator is fed to an automatic electronic potentiometer 18 provided with a calibrated filament 18a. This filament delivers a voltage proportional to the measured pressure differential AP In the present specification and claims, the term automatic potentiometer designates an apparatus measuring a voltage or electromotive force by the method of opposielectrical resistance element provided with a runner or index continuously displaceable along the resistance ele electrical output signal indicating the pressure differential tion, an equilibrium being realized automatically by a i merit. Such a resistance is frequently called a potentiometer.

The gas flow volume passing through the exhaust conduit is measured in the same manner by a pressure differential pressure gage or manometer 19, forming part of flowmeter 14. One conduit leads from the inlet of venturi 13 to one chamber of the gage while another conduit leads from the venturi output to the other gage chamber whereby the loss of pressure in the venturi is registered by the gage. In the same manner as explained hereinabove, the electromagnetic transmitter 20 is fed by an oscillator 21a at 1000 c.p.s. and its output signal is demodulated by demodulator 21b, the demodulated output signal being transmitted to automatic potentiometer 22 provided with calibrated filaments 22a delivering an output voltage AP proportional to the pressure differential of venturi 13. This output voltage does not represent the gas flow volume and it is, therefore, necessary to correct this as a function of the gas pressure, its temperature and its density, according to the following equation:

wherein Q is the gas volume, K is a numercial coefficient and w :k 9+k (CO k (0) being a correction coefficient proportional to the gas temperature at the point of measurement and k (CO which takes into account the gas density, is a coefiicient proportional to its content of CO which particularly influences its density. Correction for humidity is not effected directly because this correction is made with that of the temperature since the gas has been saturated in the dust removing humidifier.

With Equation III, the square of the gas volume is obtained directly and may thus be placed into Formula I or II designed to obtain the parameter AP,. The correction according to Equation III is effected in a servo mechanism 23 which receives signal AP from filament 22a and the correction signal Ta correlating them in a known manner by a calibrated filament 23a to whose respective ends the signals are applied, and including a zero amplifier 23b and an equilibrium motor 230 which positions the calibrated filament 23a at equilibrium. A calibrated filamerit emitter 23d delivers the coefficient k an adjustable voltage being delivered to the ends of filament 23d.

The correction coefiicient T10 itself is obtained as the output signal from an electrical adder 24 comprising an electronic amplifier 24a which receives signal k (0), on the one hand, and signal k (CO on the other hand. An adjustable resistance 24]) makes it possible to vary the proportion of the input signals k (0) and k (CO Signal k (0) comes from an automatic potentiometer 25 provided with a calibrated emitter filament 25a which receives the signal from a thermocouple 26 placed in the exhaust conduit at the inlet of venturi 13. The signal k (CO comes from a gas analyzer 27 which analyzes the gas contents by infrared ray absorption, the output signal of the analyzer being amplified by amplifier 28 before being delivered to resistance 24b.

The principal calculation according to the Equation II is effected in adder 29 comprising amplifier 29a and four adder resistances 29b, 29c, 29d and 29e of which certain ones are adjustable to enable the terms of the sum to be adjusted. The temperature of the exhausted efiiuent is measured at the outlet of the hood 2 by thermocouple 12 which controls automatic potentiometer 30 provided with calibrated filament 30a. The constant A (which is 0.55 at a temperature of 850 C., as calculated hereinabove) is delivered by a calibrated filament 31 with manual control, the filament being kept at a constant voltage. The resistances 29b, 29c, 29d and 2% receive the output signals from resistance 31, servo mechanism 23, resistance 18a and resistance 30a, the voltages of the four resistances are combined and the adder 29 delivers an output voltage through amplifier 29a, which is proportional to AP,. A definite fraction of this output voltage 2= (III) is produced by fixed resistances 32a, 32b and this is measured by automatic potentiometer 16 with its resistance 16a and amplifier 16b. In a known manner also described in the above-mentioned copending application, the pneumatic governor 17 is mounted on the mechanical axle of potentiometer 16 and this governor delivers compressed air to the exhaust suction control valve 6 through conduit 33 so as to set the valve in the desired position which keeps the automatic potentiometer 16 always at zero setting, i.e. the pressure differential AP, is kept to zero. In this manner, the electronic computer so controls the suction force in the exhaust conduit that there is no pressure differential between the efiiuent pass ing through the interspace between converter mouth and exhaust hood, and the surrounding atmosphere.

The operation of an automatic potentiometer will now be explained although such devices are well known, potentiometer 16 being taken by way of example. A socalled reference voltage is applied to a portion of calibrated filament 16a whose ends are maintained at a known constant voltage. This reference voltage is opposed to the voltage to be measured and the difference therebetween is applied to an amplifier 16b which feeds a small electric equilibrium motor 160, the latter displacing the runner of the calibrated filament 16a to seek the equilibrium. When the reference voltage is equal to the voltage to be measured, the motor stands still. The mechanical position of the runner of filament 16a thus constitutes a measure of the unknown voltage. The motor 16c may also entrain an index in front of a scale or a pen Writing on calibrated paper. The position of the runner may also be transmitted to another element, such as in the case of potentiometer 16 operating the pneumatic governor 17.

It will be noted that the constant signal introduced into adder 29 from resistance 31 is not modified. Thus, it would be possible to suppress it and to replace it by a simple displacement originating from potentiometer 16 or governor 17. The result would still be the same, the constant being ignored in the computer and the initial value of the governor no longer being set at zero (which is equivalent to permitting the constant A to pass from one side to the other in the equation).

Obviously, the above-described computer and its elements constitute only an exemplary embodiment of a control system suitable for the practice of the present invention and in no way limit the same thereto, many variations and modifications being well within the skill of the person skilled in the art, particularly after bene fiting from this teaching. For instance, the entire computation and control could be effected solely by pneumatically operated devices, i.e. bell-shaped differential manometers, pneumatic adder relays, pressure-operated transformers, etc. Also, diiferent electronic systems may be used to obtain equivalent results. For instance, automatic potentiometers for transmitting the parameters of the equation need not be used but the electric output signals corresponding to these parameters may be delivered directly to the electronic adder by suitable measuring devices. The exemplified embodiment has been used in an experimental installation where it was desired to record a great number of parameters at different points of the control circuit but this may not be necessary in many industrial installations.

Accordingly, the scope of the present invention is determined solely by the appended claims.

What is claimed is:

1. In a method of collecting a gas from an open container substantially without dilution by the ambient atmosphere, the steps of:

(a) discharging a stream of said gas from said container in a predetermined direction;

(b) receiving the discharged stream in the orifice of a hood, said orifice being spaced from said container in said direction;

arages to) passing the received stream through said hood from said orifice through an outlet of said hood to an exhaust conduit connected to said outlet;

(d) measuring the difference between the pressure of said ambient atmosphere and the pressure of said gas at a point between said orifice and said outlet in said hood, said point being spaced from said orifice;

(e) measuring the volumetric rate of flow of said gas passing through said hood;

(f) producing a control signal in response to the measured pressure difference and to the measured rate of flow; and

(g) applying suction to said stream of gas in said exhaust conduit in response to said control signal in such a manner that the difference in the pressures of said stream of gas at said orifice and of said atmosphere remains substantially zero.

2. The method according to claim 1 wherein said control signal is produced in response to a parameter AP correlated to said measured pressure difference and said measured rate of fiow by the equation wherein AP; is said difference between the pressures of said stream of gas at said orifice and of said atmosphere; AP is the ditference between the pressure of said gas within said hood at said point and the pressure of said ambient atmosphere at the level of said point; A and K are empirical constants, and Q is said measured rate of flow; and said suction is applied to said stream of gas in (B is said exhaust conduit in such a manner as to reduce AP substantially to zero.

3. The method according to claim 1 wherein the temperature of said gas in said hood is determined; and said control signal is produced in response to a parameter AP correlated to said measured pressure difference, said temperature, and said measured rate of flow by the equation wherein AB is said dilference between the pressures of said stream of gas at said orifice and of said atmosphere; AP is the diiierence between the pressure of said gas within said hood at said point and the pressure of said ambient atmosphere at the level of said point; k, A and K are empirical constants, Q is said measured rate of flow; T is a reference temperature; and T is the temperature of said gas in said hood; and said suction is applied to said stream of gas in said exhaust conduit in such a manner as to reduce AP; substantially to zero.

References Cited by the Examiner UNITED STATES PATENTS 2,855,194 10/1958 Kolnig 75-60 2,855,292 10/1958 Vogt 756O 3,154,406 10/1964 Allard 7560 FOREIGN PATENTS 872,088 7/1961 Great Britain.

BENJAMIN HENKIN, Primary Examiner. 

1. IN A METHOD OF COLLECTING A GAS FROM AN OPEN CONTAINER SUBSTANTIALLY WITHOUT DILUTION BY THE AMBIENT ATMOSPHERE, THE STEPS OF: (A) DISCHARGING A STREAM OF SAID GAS FROM SAID CONTAINER IN A PREDETERMINED DIRECTION; (B) RECEIVING THE DISCHARGED STREAM IN THE ORIFICE OF A HOOD, SAID ORIFICE BEING SPACED FROM SAID CONTAINER IN SAID DIRECTION; (C) PASSING THE RECEIVED STREAM THROUGH SAID HOOD FROM SAID ORIFICE THROUGH AN OUTLET OF SAID HOOD TO AN EXHAUST CONDUIT CONNECTED TO SAID OUTLET; (D) MEASURING THE DIFFERENCE BETWEEN THE PRESSURE OF SAID AMBIENT ATMOSPHERE AND THE PRESSURE OF SAID GAS AT A POINT BETWEEN SAID ORIFICE AND SAID OUTLET IN SAID HOOD, SAID POINT BEING SPACED FROM SAID ORIFICE; (E) MEASURING THE VOLUMETRIC RATE OF FLOW OF SAID GAS PASSING THROUGH SAID HOOD; (F) PRODUCING A CONTROL SIGNAL IN RESPONSE TO THE MEASURED PRESSURE DIFFERENCE AND TO THE MEASURED RATE OF FLOW; AND (G) APPLYING SUCTION TO SAID STREAM OF GAS IN SAID EXHAUST CONDUIT IN RESPONSE TO SAID CONTROL SIGNAL IN SUCH A MANNER THAT THE DIFFERENCE IN THE PRESSURES OF SAID STREAM OF GAS AT SAID ORIFICE AND OF SAID ATMOSPHERE REMAINS SUBSTANTIALLY ZERO. 